How to Fix Outlook Error 0x80040154 — Class Not Registered [2026]

Outlook Error 0x80040154: Class Not Registered

This error typically occurs when corrupted microsoft office installation. Below you'll find 5 proven fixes to resolve it.

What Causes Outlook Error 0x80040154?

Outlook error 0x80040154 (Class Not Registered) can be triggered by several issues:

Corrupted Microsoft Office installation
Missing or unregistered DLL files
Windows registry corruption
32-bit and 64-bit Office or component mismatch
Recent Windows Update broke COM registration

How to Fix Outlook Error 0x80040154 — Step by Step

Repair Office installation

Open Settings > Apps > find Microsoft Office or Microsoft 365 > Modify > Quick Repair. If that does not work, choose Online Repair. This re-registers all Office COM components.

Re-register Office DLLs

Open CMD as Admin and run:
for /R "%programfiles%\Microsoft Office" %i in (*.dll) do regsvr32 /s "%i"
This silently re-registers all Office DLL files.

Run the Office repair tool

Download the Microsoft Support and Recovery Assistant from aka.ms/SaRA-Download. Run it and select Outlook > I have the error 0x80040154. It performs automated repair steps.

Check 32-bit vs 64-bit mismatch

If you are running 32-bit Outlook with 64-bit Windows components (or vice versa), some COM classes may not register correctly. Uninstall Office and reinstall the version that matches your Windows architecture.

Reinstall Microsoft Office

As a last resort: uninstall Office completely using the Office uninstall support tool at aka.ms/SaRA-OfficeUninstallFromPC, restart, then reinstall from office.com.

Still Getting Error 0x80040154?

IT Cares can diagnose and fix this error remotely — usually in under 30 minutes.

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Frequently Asked Questions

What does error 0x80040154 mean in Outlook?

It means a COM class required by Outlook is not registered in the Windows registry. Outlook cannot launch a component it needs, such as the email editor or calendar.

Why did this start after a Windows Update?

Some Windows Updates modify COM registrations. A failed or partial update can leave required classes unregistered. Running Office repair re-registers them.

Can I fix this without reinstalling Office?

Usually yes. The Quick Repair option in Apps settings and the Microsoft Support and Recovery Assistant fix this in most cases without a full reinstall.

Does this affect Outlook data?

No. Your emails, contacts, and calendar are stored in .pst or .ost files and are not affected by this error or its repairs.

Is this error related to 32-bit vs 64-bit?

It can be. If you installed a 32-bit add-in with 64-bit Outlook (or vice versa), the COM class will not register. Remove incompatible add-ins via Outlook > File > Options > Add-ins.

How to Fix Outlook Error 0x80040154 — Class Not Registered